The present invention generally relates to gas supplying apparatuses and more particularly, to a gas supplying apparatus which supplies to a processing apparatus gaseous raw material including vapor of liquid raw material of an article so as to efficiently perform replenishment of the liquid raw material.
In order to manufacture a base material of optical fiber by employing VAD method, it is necessary to supply to an optical fiber reaction apparatus gaseous raw material of the optical fiber, which is constituted by carrier gas mixed with vapor of liquid raw material of the optical fiber, with the liquid raw material being silicon tetrachloride or gemanium tetrachloride.
Hereinbelow, a prior art gas supplying apparatus for supplying the gaseous raw material of the optical fiber to the optical fiber reaction apparatus will be described with reference to FIG. 1. As shown in FIG. 1, since a main vessel 2 containing liquid raw material 1 of the optical fiber is secured to a bottom portion of a constant temperature bath 3 directly or through a support base, the liquid raw material 1 is maintained at a predetermined temperature. Carrier gas 4 is introduced, through a pipe 6 provided with a flow regulator 5 and dipped into the liquid raw material 1 of the main vessel 2, into the liquid raw material 1 of the main vessel 2 so as to bubble the liquid raw material 1 as shown in FIG. 1. Thus, the carrier gas 4 is mixed with the liquid raw material 1 to a saturated state or an almost saturated state so as to be formed into gaseous raw material 7. The gaseous raw material 7 is supplied to the optical fiber raction apparatus via a pipe 8. Meanwhile, since the carrier gas 4 is not necessarily required to bubble the liquid raw material 1, it can be also so arranged that the carrier gas 4 is simply introduced over a liquid level of the liquid raw material 1 in the main vessel 2 so as to be mixed with vapor of the liquid raw material 1 into the gaseous raw material 7. The liquid raw material 1 for replenishment is stored in an auxiliary vessel 9 connected with a pipe 10. Furthermore, an inlet end 11a of a main pipe 11 is dipped in the liquid raw material 1 stored in the auxiliary vessel 9, while an outlet end 11b of the main pipe 11 is disposed in the main vessel 2 and above the liquid level of the liquid raw material 1 in the main vessel 2. Moreover, the known gas supplying apparatus includes control valves 12 to 18.
In the known gas supplying apparatus of FIG. 1, in order to supply the gaseous raw material 7 to the optical fiber reaction apparatus, the control valves 12 and 13 are opened. Meanwhile, when the gaseous raw material 7 is continuously supplied to the optical fiber reaction apparatus and thus, the liquid raw material 1 stored in the main vessel 2 decreases in amount, the main vessel 2 is replenished with the liquid raw material 1 stored in the axuiliary vessel 9. In order to replenish the main vessel 2 with the liquid raw material 1 stored in the auxiliary vessel 9, the control valves 14 and 17 are closed and the control valves 15, 16 and 18 are opened, while pressurized nitrogen gas 19 is fed into the auxiliary vessel 9 through the pipe 10. Thus, the main vessel 2 is replenished, through the main pipe 11, with the liquid raw material 1 in the auxiliary vessel 9 by the pressurized nitrogen gas 19. It is to be noted that the above described replenishment of the liquid raw material 1 into the main vessel 2 is referred to as a "primary replenishment", hereinbelow. When the main vessel 2 has been replenished with a predetermined amount of the liquid raw material 1 in the auxiliary vessel 9, the open control valves 16 and 18 are closed and the closed control valve 17 is opened. Thus, the liquid raw material 1 remaining in the main pipe 11 is fed under pressure into the main vessel 2 by the pressurized nitrogen gas 19. It is to be further noted that this replenishment of the liquid raw material 1 into the main vessel 2 is referred to as a "secondary replenishment", hereinbelow. Subsequently, when the control valve 15 is closed and the control valve 14 is opened, namely the control valves 15, 16 and 18 are closed and the control valves 14 and 17 are opened, the pressurized nitrogen gas 19 is further fed into the main pipe 11 so as to drive a small amount of the liquid raw material 1 remaining in the main pipe 11 out of the main pipe 11 through the control valve 14. Meanwhile, when the main vessel 2 is being replenished with the liquid raw material 1 stored in the auxiliary vessel 9, supply of the gaseous raw material 7 to the optical fiber reaction apparatus is stopped. Furthermore, although not specifically shown, it has been also so arranged that a plurality of the main vessels 2 are replenished with the liquid raw material 1 stored in the single auxiliary vessel 9.
However, the prior art gas supplying apparatus of FIG. 1 has the following drawbacks (1) and (2). (1) In the case where the single main vessel 2 is replenished with the liquid raw material 1 in the single auxiliary vessel 9:
A total replenishment amount of the liquid raw material 1 should be set on the basis of two replenishment amounts of the liquid raw material 1 based on the primary replenishment and the secondary replenishment, thereby resulting in difficulty in setting the total replenishment amount of the liquid raw material 1. Furthermore, in the case where the main pipe 11 is replaced with a new one having a length and a diameter different from those of the main pipe 11, the replenishment amount of the liquid raw material 1 based on the secondary replenishment directly changes accordingly, so that it becomes necessary to set the total replenishment amount of the liquid raw material 1 again, which is a troublesome operation. (2) In the case where a plurality of the main vessels 2 are replenished with the liquid raw material 1 in the single auxiliary vessel 9:
Since a plurality of the main pipes 11 connecting the main vessels 2 and the auxiliary vessel 9, respectively have lengths different from one another, the replenishment amounts of the liquid raw material 1 for the respective main vessels 2 based on the secondary replenishment are different from one another. Accordingly, when amounts of the liquid raw material 1 in the respective main vessels 2 should be set at a predetermined value, the replenishment amounts of the liquid raw material 1 for the respective main vessels 2 based on the secondary replenishment are required to be set at different values for the main vessels 2, respectively, which is quite troublesome. Especially, in the case where a number of the main vessels 2 are scattered at various spots with the result that the long main pipes 11 are installed complicatedly, the above described disadvantage of the known gas supplying apparatus becomes quite serious.